RF Splitter/Combiner ??

I have a pile of ChannelPlus Model 2509 Splitter/Combiners __________________ ____| |____ |____| IN OUT |____| | | | | | -9dB TAP | |__________________| | | | | |__|

I understand the Splitter function, but how does it behave as a Combiner?

If I insert a signal into the TAP, how much back-feed do I get in the main source? (In those conditions I believe you swap the IN/OUT ports ??) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson
Loading thread data ...

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

These are usually directional couplers. It has a 9 dB loss to the tap port, a very low loss from in to out ports. The tap port has isolation to the out port, maybe 20 dB or more.

Do you have any RF test equipment? If not, you can send me one and I can measure it for you.

Regards

Reply to
Tom Miller

Either way it will behave reciprocally, there are only a few (expensive) RF components that are non-reciprocal.. (circulators and isolators) and they utilize non linear properties of ferrite and magnets.

If this is a cheap CATV device it willnot have these.

But it could be a true directional coupler in which case if you feed a signal into the -9dB out, it will flow back with 9 dB loss to the IN port and less so to the OUT port.

If it is a simplresistive splitter, the signal will flow backwards equally at -9dB to the IN and OUT.

Mark

Reply to
makolber

As has been said, it depends on whether it's a simple resistive splitter or uses ferrites and magnets.

Grind one open and see. Post pics.

Mark L. Fergerson

Reply to
Alien8752

As soon as you say RF, I think minicircuits.

formatting link

The inside of a ZSC-2-2.

formatting link
(I tried to trace out the transformer wires one day and gave up.)

George H.

Reply to
George Herold

It is not a practical combiner. It is more likely that there are 3 dB splitters in the same family of products that are combiners and they are just calling the whole family of products combiner/splitter.

Reply to
bulegoge

You have two different things mixed together. There are splitter/combiners and directional couplers. They're quite different.

  1. A splitter divides the signal in half, adds about 0.5dB of internal loss, and delivers the same signal to each of the output ports at -3.5dB level. On some splitters, there will be -3.5dB printed on the label near each output port.

When used in the other direction, as a combiner, it will take two RF signals (not necessarily identical), add them with only about -0.5dB loss, and deliver them to the single output port at about 1dB combined power loss. It can do this because there is at least 20dB isolation between the two input ports, so there's no power loss caused by loading from the other input, or from a mismatch.

Of course, there are various ways to design the splitter, some good, some not so good:

  1. Your drawing above, with the -9dB tap is called a directional coupler. It couples some signal from the input port with a -9dB loss, and as little as possible from the output port. There's also very little loss between the input and output ports. Taps are mostly used in houses where the CATV wiring was done in the same manner as telephone wiring (single cable daisy chained around the house instead of "home run").

If your palatial mansion has a single run of cable around the perimeter, and you have 5 TV's, the signal to each TV would be down

-9dB from whatever it's being fed (minus any coax losses). The same arrangement done with -3.5dB splitters would yield: split loss 1 -3.5dB 2 -7.0dB 3 -10.5dB 4 -14.0dB 5 -17.5dB The first 3 TV's would work, but the one's running on the 4th or 5th splitter would probably not have enough signal. Taps will also cause problems for devices that require talking to devices that might be in the reverse direction of a tap, such a MoCA data modems.

As for what goes on inside the splitter or tap, bug me later. I'm late for lunch (again).

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

I'm interested on quantifying its behavior as a _combiner_ ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

Oh, that's easy. You can't use a tap or directional coupler to combine signals. It won't work unless you're willing to tolerate lots of loss and possibly a mismatch.

Inside the magic box is the equivalent of a transmission line (input to output) and a parallel transmission line that's about 1/4 wavelength long, which is terminated on one end, and connected to the tap port on the other. The degree of coupling is dependent on the proximity of two transmission lines. It's the same as what makes a cheap VSWR meter work. If you apply RF to the input and output ports, you get a short circuit between ports. If you apply power to the tap port, it all get converted to smoke in the internal terminator with very little going to the input and output ports. In other words, it ain't gonna woik as a combiner.

Perhaps it might be helpful if you disclose what you're trying to accomplish?

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

The above is WRONG. ( I wish it were true, I you know how to make this true, email me and we will become millionares)

A 2 way passive hybrid combiner will always have at least 3dB of loss to each signal except under one very special condition......and that is when the two signals being combined are identical.

The extra 3dB loss is dissipated in the internal resistor.

When a combiner is used in a transmitter two combine multiple transistors for example, the two signals are the same and there is no voltage across the internal resistor and hence no loss (ideally).

If one transistor should fail, the Tx output then goes dowen by 6 dB, (not 3 dB) becasue you loose the output of one transistor and the combiner loss is now 3 dB.

Mark

Reply to
makolber

I want to insert a signal that only feeds forward, not back into the main source.

The box says CP-2509 Tap/Combiner. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

best to use an amplifer which has reverse isolation at least equal to its gain

Mark

Reply to
makolber

Identical in frequency and phase. There is a 3dB loss to each signal if the two signals are uncorrelated. If the two signals are identical then phasing tells the whole story about overall loss.

Reply to
bulegoge

I've seen them used as such, combining a satellite tuner's UHF RF output with a weak local UHF TV reception, where running the TV antenna throught the sat box's RF in would cause too much loss.

inside there's a lossy transformer between the thru conductor and the terminated tap conductor, most of the power put into the tap is going to end up in the termination resistor, but some will couple onto the thru.

I don't have numbers.

--
  \_(?)_
Reply to
Jasen Betts

I successfully trashed my reputation by suggesting exactly the same thing and had to be corrected by those that know more about such things.

Try a simple experiment. Take a common splitter. Put some kind of signal level measuring contrivance on the common port. Apply some RF to ONE of the split ports. Terminate the remaining split port. You should get about the same out of the common port as you put into one of the split ports. Obviously, reversing the two split ports will produce the same level. In short, there's no loss in the combiner configuration because the split ports are isolated from each other by about 20dB.

A Wilkinson combiner is much the same thing. There's a 90 degree phase shift in each of the 1/4 wave lines, resulting in 180 degrees of phase shift between the splitter ports with a 50%(?) drop in signal level. The impedance seen across those is twice 50 ohms (or 75 ohms for the CATV flavor). 100 ohms (or 150 ohms) between the ports yields an in-phase signal at 180 degrees otto phase, resulting in almost total cancellation and the -20dB or so isolation.

However, your example of combining two transmitters requires a 0 or

180 degree hybrid coupler and that the fourth port of the coupler be present and terminated. Instead of the reflected RF produced by an imbalance being dissipated in the power amplifier(s), it is dissipated in the termination. In other words, the transmitter combiner is very different from whatever Jim is trying to accomplish.

Sorry for the rambling...

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

No problem. The injected signal goes into the -9dB tap port and is terminated by the internal terminator. If you take an ohms guesser and measure the resistance to ground on this port, methinks you should see 75 ohms. The signal then appears at the INPUT port, but -9dB down in level. You should see nothing on the OUTPUT port if both the INPUT and OUTPUT ports are terminated with either a 75 ohm terminator, or by the input/output impedance of a spectrum analyzer or RF generator.

I can try it with a signal generator and spectrum analyzer if you want, but only after I clear the table from the current project probably by this weekend.

I'm wondering what you're really doing. Perhaps you're injecting an RF signal backwards into the cable which could produce intermodulation products and junk which ruin the cable picture? That's called "ingress" or cable leakage and is not a good thing. Are you sure that you want to do this?

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

The "cable" is the "source" that I don't want to back-feed. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

You should be ok doing with a directional coupler (tap) as long as your inside cable is properly terminated. That means every splitter and divider along the line has a 75 ohm terminator on every unused port, and that every device that's attached presents a proper 75 ohms to the cable. The problem is VSWR. If the cable were not properly terminated, the reflected signal off any mismatched port will reflect back towards the source and eventually end up going back towards the cable drop. The tap will provide isolation for anything going from INPUT to OUTPUT (or for that matter, from OUTPUT to INPUT).

However, I think you might be better off with either a unidirectional (CATV only) or bi-directional (CATV and cable modem) amplifier set to fairly low gain. It will do a much better job of isolating your mess from the cable companies equipment and a tap. The one's that are adjustable will go to zero gain. If you get one that has, for example

15dB gain, you can just cram a -15dB attenuator on the output(s) to reduce the gain.
--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Oh, so you want a 75 Ohm broadband directional coupler... The critical spe c is the directivity...

formatting link

But it does does not always work that way in practice, especially if you g et your internet over the cable... Ie your cable modem sends "reverse" cha nnels to the head end..

SO, assuming you do not have cable internet and your set top box does not " talk" to the head end, The classic method would be use a broadband 75 ohm isolation amplifier followed by a splitter used in reverse to sum the sign als... Then send that out into your house.

But that is the way it would be done in the olden days, modern boxes are bi directional for the most part and need to talk to the head end.. Making thi s idea a non-starter in most cases.

Need many, many more details if your doing this a CATV system, is this a on e-off or a product?

It is unlikely you can do this on a modern CATV system without getting into problems with creating IMD on your local cable system for MANY of your nei ghbors.

Steve

Reply to
sroberts6328

true, email me and we will become millionares)

o each signal except under one very special condition......and that is when the two signals being combined are identical.

I'm sorry you are wrong.

A hybrid combiner as shown in Fig 16 here (just to make sure we are talking about the same thing)

formatting link

CANNOT combine 2 different signal without loss.

It can combine 2 signals without loss ONLY if the 2 signals are coherent wi th each other.

In fact, there is NO passive broadband device that can combine signals wi thout loss.

(Yes it can be done with amplifiers or with frequency selective filter netw orks but we are talking about passive broadband circuits here.)

In Fig 16, if you terminate P3, and feed 0 dBm into P2, there will be -3dB m at P1 and there will be -3dBm dissipated in the resistor. Of course the result is the same if you transpose P2 and P3. The device will be a lossl ess combiner ____ONLY___ if you feed P2 and P3 with 2 coherent signals (in verted polarity in this case. In this case, no power is lost in the resist or.)

Mark

Reply to
makolber

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.